1. Field of the Invention
The invention mainly relates to the seismic-resistant beam-to-column connections for use in the moment-resisting steel frames comprising beams and columns.
2. Description of the Prior Art
Steel structures are recognized to be capable of developing the required strength and ductility to resist the earthquake loading because of the ductile material property of the steel. Steel moment-resisting frames can provide excellent inelastic behavior under severe seismic loading. The inelastic behavior of a ductile steel moment-resisting frame is mainly attributed to the plastic deformations of the connections formed between beams and columns. Therefore, the beam-to-column connections shall be designed appropriately to have sufficient strength and inelastic deformation to dissipate large portion of the energy imposed from the earthquake.
The beams used in the present invention are typical I-shaped and wide flange sections. The conventional connections of the beams to columns are commonly achieved by bolted web and welded beam flanges to column flange. The weld between top and bottom beam flanges and column flange is usually a full penetration weld and performs in the field. Moreover, two fan type weld access holes in the beam web near the flange are needed to perform this full penetration weld. The presence of those weld access holes in the beam web causes the stress concentration near the center of the beam flange. As a result, brittle failure can occur in the connections because of a variety of influences, such as weld defect, weld access hole, and stress concentration.
These widely used conventional beam-to-column connections were found failed in suffering the catastrophe after the ruthless test of Northridge earthquake in 1994. The failures of the connections include the buckling and fracture of the flange and web of the beam and column, fracture of the shear tab, and weld tearing between beam and column. The observed damage prevented the welded beam-to-column connections from the intended inelastic behavior to resist earthquake ground shaking.
Numerous researches were, then, undertaken to improve the behavior of such beam-to-column connections of the previous art. Some modified moment connections have been developed to upgrade and to resist seismic demands through the improvement of the inelastic behavior of the connections. The recent improved connections include the strengthened connections and reduced beam section connections.
It is the object of present invention to provide a steel structure that has stable strength and stiffness and maintains its integrity through inelastic deformation during severe earthquake. The present invention is to guarantee an excellent inelastic behavior of the beam-to-column connection.
This aim is achieved by providing an improved beam-to-column connection. The improved connection reduces the stress concentration of the beam flange caused by the weld access hole. This stress concentration causes the potential cracking initiated in the root of the weld access hole and the cracking will spread and tear the weld. As a result, the connection will fail in a brittle manner. The improvement of present invention is to provide evenly distribution of the stress across the connection.
The present invention is further to provide the occurrence of the plastic hinge of the beam under a severe earthquake away from the surface of the column. The formation of the plastic hinge of the beam away from the column flange results in the assurance of the large plastic rotations that permit hysteretic dissipation of earthquake-induced energy.
The present invention is furthermore to increase the plastic rotation capacity through the guarantee of the presence of an extended energy dissipative zone in the beam. The seismic-resistant ability is enhanced through the use of the improved connection that is demonstrated and based upon the discovery of non-linear finite element analysis as well as full-scale structural experiment.
For more detailed information regarding this invention together with further advantages or features thereof, at least an example of preferred embodiment will be elucidated below with reference to the annexed drawings.